Boom mower attachment for a tractor adjustable for cutting at either side thereof

ABSTRACT

A boom attachment which carries a work unit pivotally at its outer end and which is pivotally connected at its inner end to an upstanding support carried by a base is attached to the rear end of a tractor by a three-point hitch and is operated from a power take-off on the rear of the tractor. The boom is adjustable in a transverse plane at the rear of the tractor so that the work unit can be disposed at either side of the tractor without removing or replacing parts in making this adjustment. This adjustment is accomplished with a cylinder and piston unit which is connect at the side of the boom by outwardly extending pivots.

REFERENCE TO OTHER CASES

This application is a continuation-in-part of application Ser. No.228,232, filed Aug. 4, 1988, now U.S. Pat. No. 4,912,916 which is acontinuation-in-part of application Ser. No. 156,816, filed Feb. 17,1988, now U.S. Pat. No. 4,887,417.

FIELD OF INVENTION

This invention relates to an attachment to a tractor having a boom whichsupports a work unit such as a mower or flail cutter or other types ofwork units. In the present description the work unit is referred to as amower but it obviously can be other work units or tools supported on theouter end of the boom. The boom is mounted on the rear end of anordinary tractor by means of the usual three-point hitch and powertake-off connection.

PRIOR ART

Many types of attachments have been provided in the prior art consistingof a boom which is mounted on the rear end of a tractor by a three-pointhitch and power take-off. These attachments usually consist of a boompivotally connected to the tractor for swinging vertically. The outerend of the boom has a work unit such as a mower or flail cutter headpivoted thereto. The main disadvantage of these prior art attachments isthat they can cut or work at one side only of the tractor. To changesides, if at all possible, it is necessary to remove the attachment fromone side and remount it on the other side which is burdensome andtime-consuming.

SUMMARY OF THE INVENTION

The present invention in its preferred form provides an articulated boomattachment consisting of at least two sections pivoted together with theinnermost section pivotally mounted on the rear end of a tractor with athree-point hitch. The outer end of the outer section of the articulatedboom carries a work unit such as a mower which is pivotally connectedthereto. The pivoting of the articulated boom sections relatively andrelative to the tractor is controlled by connected cylinders which arepart of a hydraulic system powered from the power take-off of thetractor. The arrangement of the articulated boom and connected cylindersis such that the boom can swing through a vertical arc of about 210° toposition the mower at either side of the tractor so that mowing can beat either side of the tractor without any disconnecting or remounting ofparts.

In another form of the invention the attachment uses a single sectionboom which has the mower or other work unit pivoted to its outer end anddriven by a belt and pulley arrangement extending along the boom. Theinner end of the boom is pivoted at the usual tractor hitch for swingingmovement through about 210° in a transverse plane at the rear of thetractor. This swinging movement is accomplished by a cylinder and pistonunit as in the preferred form which is connected to the support and tothe boom at outwardly extending pivots so as not to interfere withswinging movement of the boom. Since the drive and mounting will notinterfere with this swinging movement the boom can swing to one side orthe other for cutting or other work at either side of the tractorwithout removal and replacement of parts.

BRIEF DESCRIPTION OF THE DRAWINGS

The best mode contemplated in carrying out this invention is illustratedin the accompanying drawings in which:

FIG. 1 is a side elevational view showing the preferred form of theattachment of this invention supported on the rear end of a tractor;

FIG. 2 is a view of the rear end of the tractor with the articulatedwork unit supporting boom extending at the right-hand side of thetractor to support the work unit in the form of a mower in a horizontalposition;

FIG. 3 is a view similar to FIG. 2 with the boom extending at theleft-hand side of the tractor;

FIG. 4 is a view similar to FIG. 2 but showing the articulated boomadjusted to support the mower in an inclined position such as on a steepbank;

FIG. 5 shows the articulated boom being moved from the right-hand sideto the left-hand side over the center of the tractor towards a positionwhere the mower will be at the left-hand side of the tractor;

FIG. 6 is an enlarged sectional view taken through the mower or workunit support and showing means for adjusting the angle of the mower onits support;

FIG. 7 is a plan view of the tractor and attachment showingschematically how the safety breakaway joints at the tractor mount forthe boom to permit yielding if the mower strikes an obstruction;

FIG. 8 is an enlarged right-hand side elevational view showing theattachment in upright position on the tractor for transport;

FIG. 9 is an enlarged detail in side elevation showing one of the safetybreakaway joints;

FIG. 10 is a side elevational view showing one form of mower which maybe mounted on the articulated boom;

FIG. 11 is a vertical sectional view taken along line 11--11 of FIG. 10;

FIG. 12 is a horizontal sectional view taken along line 12--12 of FIG.11;

FIG. 13 is a rear elevational view showing a different form of theinvention using a single section boom;

FIG. 14 is a plan view of the attachment of FIG. 13;

FIG. 15 is a side elevational view showing the mower and the drive forthe mower;

FIG. 16 is a fragmentary rear elevational view of the connection andbrake system between two arms of the boom;

FIG. 17 is a side elevational view of FIG. 16;

FIG. 18 is a side elevational view of the connection and brake systembetween the outermost arm of the boom and the cutter head;

FIG. 19 is a sectional view taken along line 19--19 of FIG. 18;

FIG. 20 is a side elevational view of a preferred cutting head;

FIG. 21 is a front elevational view of the head of FIG. 20; and

FIG. 22 is a bottom plan view of the head of FIG. 20.

DETAILED DESCRIPTION OF THE INVENTION

With reference to the drawings and specifically to FIGS. 1 to 5, 7 and 8there is shown an example of a tractor 20 which is a standard type andhas a three-point hitch arrangement of support arms 21 at its rear forsuspending the attachment 22 of this invention for forward and rearwardpivoting about a transverse horizontal axis at rod 23 (FIG. 7). Thetractor has a hydraulic pump 25 which is attached to the power take offof the tractor 20 and is connected to the hydraulic system of theattachment by lines (not shown) in a conventional manner.

As previously indicated the preferred form of the attachment 22 ismainly in the form of an articulated boom consisting of at least twopivotally connected sections which are indicated in FIGS. 1 to 7 of thedrawings as an inner section 26 and an outer section 27. The twosections are pivoted together for relative swinging in a transversevertical plane by means of a pivot joint or pivot located at 28 betweentheir adjacent ends. The inner end of the inner section 26 is pivoted bya similar pivot joint 29 to the upper end of an upright pedestal support30 which extends upwardly from a support base 31. Each of the pivots 28and 29 are similar consisting of a pair of pivot brackets 32 (FIG. 8)welded to one section which straddle the adjacent end of the othersection and receive a transverse pivot pin 33. With this arrangement thesections 26 and 27 can swing relatively about the pivot 28 and the innersection 26 about the pivot 29 in a common vertical plane transversely ofthe tractor.

A suitable reservoir 35 for hydraulic fluid with baffels or fins 35a toaid in cooling of fluid is supported directly behind the pedestalsupport 30 by means of a pair of laterally-spaced upright brackets 36which are supported in upstanding positions on the base 31. A pair ofjacks or vertically adjustable supports 37 are attached to the reservoirat opposite vertical sides and are adapted to be used in hitching to andunhitching the attachment 22 from the tractor 20. The supports 37 may beadjustable to a level suitable for the attachment 22 to be easilyconnected to the tractor. After connecting the attachment to the tractorthe supports 37 may be retracted vertically to avoid obstructions on theground while the tractor is moving.

The reservoir is connected in the hydraulic system along with ahydraulic control box 38 mounted on the support 39 with an electriccontrol unit which is activated by a control panel 40 on the tractor.

The outer end of the outer section 27 of the articulated boom 22 carriesa work unit 41 which may be a mower or flail cutter powered by ahydraulic motor 42. Preferably the motor is connected in the hydrauliccircuit controlling the boom orientation. Other types of work units maybe used. The work unit is pivotally mounted on the outer end of the boomsection 27 for swinging through an angle of about 210°. This mounting isbest illustrated in FIGS. 6 and 7 and includes a gear and pinionarrangement for positively adjusting the angle of the work unit relativeto the boom end and holding it in adjusted position. Thus, the housingof the unit 41 has a shaft 45 rigidly carried thereby and extendingrearwardly therefrom transversely through the hollow boom section 27(FIG. 6). Within the section 27 this shaft has a pinion 46 keyed thereonwhich meshes with rack 47 reciprocably mounted in a slot 48 in the wallof section 27 by means of a slide 49. This slide 49 is connectedpivotally to a hydraulic cylinder and piston unit 50 at 50A, thecylinder of which is fixed to the outer side of the boom section 27.Thus, actuation of the cylinder and piston unit 50 will move the rack 47to rotate the pinion 46 and shaft 45 to adjust the work unit to thedesired angle about the axis of the shaft 45.

The cylinder and piston unit 50 is connected in the hydraulic circuitwith various other units including a cylinder and piston unit 51 forcontrolling relative swinging of boom sections 26 and 27 about the pivot28 and a cylinder and piston unit 52 for controlling swinging of theinner boom section 26 about the support pivot 29. Each of the units 51and 52 is similarly mounted at one side of the respective articulatedboom sections 26 and 27 and support 30 rather than in the angles betweenthose members to permit relative movement past center when desiredwithout interference from the cylinder and piston units. These units areshown in a transverse plane at the rear of the boom parallel to that ofthe boom. Unit 51 as clearly seen at unit 26 has its cylinder pivoted tothe boom section by a laterally outwardly or rearwardly extending pivot53 (FIGS. 2 and 3) mounted in the boom section approximately midway ofits ends and its piston rod pivoted by a similar pivot 55 to theadjacent boom section 27 adjacent its inner end. Cylinder and pistonunit 52 is similarly connected to boom section 26 and support 30, thepivots being indicated at 56 and 57. Thus the sections 26 and 27 can beswung relatively about the pivot 28, and the section 26 can be swungabout support pivot 29 by selective actuation of the side-mountedcylinders and piston units 51 and 52 without interference wit theseunits even if the respective members are brought into alignment at acenter position or beyond. Thus with this arrangement the articulatedboom sections 26 and 27, with the work unit 41 properly positioned, canbe moved relatively almost 180° in either direction and, the innersection 26 can be moved similarly relative to its support 30 in eitherdirection, all in a common plane transversely at the rear of the tractor20.

The attachment 22 may be in upright position at the rear of the tractor20 as shown in FIG. 8 being held in that position by unit 60. This unit60 has its front end pivoted at 61 to one of the tractor hitch pointsand its rear end pivoted at 62 to the front side of the support 30.Adjustment of the unit 60 will swing the entire attachment 22 about theaxis of the rod 23 carried by the hitch 21. The vertical position shownin FIG. 8 is desirable for transportation. Stabilizers (unnumbered)extend between rod 23 and pin 61 to control height and strengthen themounting on tractor 20.

It is desirable to have what is termed in the art as a breakawayconnection between the hitch 21 and the base 31 of the attachment topermit rearwardly yielding of the attachment in case the mower 41 wouldstrike a pole P or other obstruction as indicated in FIG. 7 during themowing operation. This breakaway connection is indicated more in detailin FIGS. 8 and 9 and includes a pair of breakaway joints at the oppositesides of the base 31. This base 31 has rigidly attached to it at itsopposite sides the vertical support brackets 65. Each bracket has arocker arm 66 pivoted at 67 inwardly of the cooperating bracket forrocking movement. A lug 68 is welded to the outside of bracket 65 andextends forwardly therefrom as a guide for the arm 66. The upper ends ofthe rocker arms 66 carry the pivot rod 23 at the hitch 21. The rockerarms 66 with the rod 23 carried thereby are normally biased rearwardlyby springs 69 adjacent the respective arms. Each spring is anchored at70 at its rear end to the bracket 65 and has its forward end connectedat 71 to the associated rocker arm 66. With this arrangement if themower 41 strikes an obstruction such as pole P, the connection at therod 23 at that side will yield as indicated in FIG. 7 to prevent damage.The same will happen when mowing at the opposite side. This also gives abreakaway when the mower 41 is backed into an object such as a polecausing the opposite side rocker arm 66 to yield so protecting bothforward and reverse movement.

FIGS. 10 to 12 show a type of mower which can be used in the attachment22. This mower 41a is mounted on the shaft of a hydraulic motor 45awhich is carried by the outer boom section 27 by means of a U-shapedbracket 27a. The mower includes housing 75 which is mounted by bracket76 for swinging movement about the axis of the motor 45a. On the housing75 is mounted a hydraulic drive motor 77 which is connected in thehydraulic circuit of the attachment along with motor 45a. A pulley drive78 leads from the motor to a series of laterally spaced spindles 79which are mounted in the housing 75 and depend therefrom where they havecutting blades keyed thereon. A feature of this mower is that adjacentblades are at different levels so that the blades 80 can overlap asindicated to fully cover the area to be cut without uncut streaks. Thehousing has runners 81 at each side and intermediate support rollers 82to govern the height of cut of the mower.

FIGS. 20 to 22 show an alternative structure for the mower of FIGS. 10to 12. Rollers 100 at each side of the housing 75 are substituted forthe runners 81. The several cutting blades in each unit extendhorizontally from a central hub 101.

A flat, generally horizontal shield 102 has been added to the forwardpart of the housing 75 and it serves two purposes. The first purpose isto block vertically propelled rocks, sticks and the like which may belaunched by the rotating blades 80. The second purpose is to projectforward of blades 80 to thereby engage stumps, posts and the like beforethe blades encounter such damaging obstructions. It will be noted inFIGS. 20 and 22 that the blades project forwardly of the housing througha slot by about three to six inches.

The belt drive illustrated in FIGS. 11 and 12 is also used in the FIGS.20-22 embodiment. Thus, the blades all rotate in the same direction.

During the course of field testing the embodiment illustrated in FIGS.10-12 long grass and weeds tend to be drawn into the housing and wraparound spindles 79. To prevent this problem a guide and deflector bar104 is added between the front of the housing 75 and the blades 80. Bar104 extends downward to within about one-half inch of the upper set ofblades.

Because the blades all rotate in the same direction and because of thenarrow gap between the bar 104 and blades 80, the severed vegetationcollects on the exterior front of the housing and the blades pump it toone side like a conveyor belt. In this instance the grass moves fromright to left as seen in FIG. 22.

Unfortunately some grass collects and winds around the spindle 106 atthe far left side. To minimize that effect, the deflector bar 104 iscurved, at 108, at the left side. A 90 turn by bar 104 is almostcompleted at the maximum point of blade extension to the left fromspindle 106.

As a result of the added deflector bar 104 combined with the otherapparatus, each pass of the cutter head leaves a heaped row of grassclippings discharged along slopped surface 108 which may be easilycollected if desired.

Another feature of the blades 80 is that they are flat in contrast toconventional blades which have upturned edges. Conventional blades arenormally surrounded by their housing and the rotating blade withupturned edges creates an updraft which pulls grass stems upward to becut. The severed grass clippings are also drawn upward above the cuttingblade and expelled radially from the housing. In the present embodimentthere is no upturned edge on the blade 80 and no updraft. The resultingcut is of the grass as it stands naturally. Consequently the visualappearance of the cut lawn is one of an essentially uniform surface inspite of the fact that the overlapping blades are vertically offset.

With the attachment 22 described it will usually be transported in theupright condition shown in FIG. 5. To use it to mow a horizontal area itmay be swung to the right as indicated in FIG. 2. With the mower 41horizontal at the right cutting head 41 be adjusted to illustratedposition by the rack and pinion 46, 47 operated by cylinder and pistonunit 50. Or the attachment may be swung to the left as indicated in FIG.3. If it is used to mow a steep bank at the right as indicated in FIG. 4the mower 41 will be angled properly by the rack and pinion adjustment.A similar adjustment will be made if a steep bank to the left is to bemowed. The adjustment of the articulated boom in a transverse planethrough an angle of about 320° is possible because of the arrangement ofthe cylinder and piston units 51 and 52 at the side of the boom ratherthan in the angles or knees between the pivoted boom sections 26 and 27and support 30. This is indicated by a comparison of FIGS. 4 and 5. Inswinging to the left from the position indicated in FIG. 2, the cylinderand piston unit 51 will gradually straighten the sections 26 and 27until they are at center or in alignment. Piston unit 52 will lowersections 26 and 27 until mower 41 contacts the ground, causing sections26 and 27 to go out of alignment. Piston unit 51 can then pull section27 toward section 26 as indicated in FIG. 4. At the same time thecylinder and piston unit 52 will move the section 26 upright and theposition of mower 41 will be reversed by the rack and pinion control tothe position shown in FIG. 5. Movement of the section 27 past centerwill cause the mower 41 to provide a gravity pull to move piston unit 52by center enabling it to move the articulated boom to the position shownin FIG. 3. Thus the articulated boom can position the mower at one sideor the other, it being moved to a center position by the cylinder andpiston units and then to a lowered position by the aid of gravity. Thesemovements through about 210° are permitted without the units interferingwith the boom and support actions since they are located to one sidethereof.

Another arrangement of a similar attachment 22a at the rear of a tractor20 is illustrated in FIGS. 13 to 15. The attachment in this instancecomprises a single boom 85 which is pivoted to the upstanding support 30at the rear of the tractor at a drive shaft 86 leading rearwardly fromthe power take-off of the tractor. The hitch 21 is the same as beforeand the breakaway pivots are provided at the ends of the rod 23. Theinner end of the boom 85 is pivoted at shaft 86 to the upper end of thesupport 30. A cylinder and piston unit 87 is mounted and connected likeunit 52 at the rear side of the boom 85 and by outwardly extendingpivots controls movement of the boom 85 about the drive shaft, pivotpoint 86, being mounted at the side of the boom so as not to preventswinging thereof through an angle of about 210° from one side of thetractor to the other. Cylinder and piston unit 87 is in a transverseplane parallel to that of boom 85, that is, behind it. The drive shaft86 drives a belt 88 and pulley 89 arrangement at the front side of theboom 85 which is connected to the drive shaft 92 of a mower 41b whichmay be like the mower 41A previously described.

With this arrangement, the boom 85 can swing through a vertical planetransversely of the tractor without the belt 88 and pulley drive 89 onthe cylinder and piston unit 87 interfering therewith. The boom canswing through an angle of about 210° so that the mower 41b can bepositioned at either side of the tractor without removing and replacingparts.

To explain the swinging action of the boom 85 when it is desired toswing from the right hand side as shown in FIG. 13 to the left handside, the hydraulic system is actuated to elongate piston unit 87. Theupper end of the unit 87 is slidably connected to the boom 85 in a slot90. As the unit 87 elongates its connection in slot 90 slides outwardlytoward mower 41b and when the connection reaches the outer limit of slot90, continued unit elongation will elevate boom 85. Rotation of the boom85 about the shaft or pivot point 86 as unit 87 elongates will continueuntil the mower 41b moves its center of gravity past a vertical lineextending through the axis of shaft 86. When that occurs the force ofgravity will rotate the boom 85 until the unit connection in the slot 90stops rotation when it reaches the innermost end of slot. Any furtherrotation of the boom toward the left is accomplished by a contraction ofunit 87. In this particular embodiment the hydraulic fluid for actuatingunit 87 is a part of the fluid system of the tractor whereas theembodiment of FIGS. 1-12 has its own separate hydraulic system.

It will be clear to tractor operators and those observing the drawingsthat in the pivoting of the boom from one side to the other, to get thegravitational assist indicated in the above paragraph, the mower 41bshould be oriented to be on one side of the boom. When the boom ismoving to the left, the mower should be to the left of the boom and whenthe boom is moving to the right, the mower should be to the right of theboom.

A hydraulic motor 45b is carried by the bracket 85a attached to theouter end of boom section 85 and the shaft thereof extends looselythrough the center pulley 89 and is attached to the bracket 76a by anoff-set, U-shaped unit 91 to swing it about the axis of motor 45b so asto adjust the entire mower 41b about that axis. Shaft 92 driven bypulley 89 in turn drives a gear box 93 which is mounted on the mowerhousing 75a driving mower blades 94. Thus hydraulic motor 45b adjuststhe mower on the outer end of the boom section 85 and the belt 88 andpulley arrangement 89 drives the mower blades.

In the pivoting of the boom from one side of the tractor to the otherside it is desirable to prevent the boom from falling too vigorouslyafter the cutting head passes the center of gravity. Looking at FIG. 5and considering the single boom section 85 of the embodiment of FIGS.13-15, when the boom 85 passes the gravitational center point it will bein free fall until the rotation picks up the slack of slot 90. Theimpact of the free fall tends to bend and whip the structural elementsof the attachment. To dampen the impact or free fall, a braking systemhas been provided at the pivot point 86. An arm 95 is secured to thebracket plate 96 connecting boom 85 to support 30 and over pivot bolt86. On support 30 a friction brake 97 is bolted or otherwise secured tofrictionally retard the motion of arm 95 (and thus boom 85) as boom 85passes the centerline in its vertical arc from one side of the tractorto the other. The frictional engagement is illustrated in FIG. 17 as apair of friction pads 98 which press against the lower end of arm 95 asit rotates to slow its rotational speed, thereby minimizing mechanicalimpact and strain due to free fall of the boom after the cutting headpasses the gravitational centerline.

Another brake 99 is built into the system and it is to prevent movementof the cutting head. With all of the moving parts, belt drives,hydraulic drives, etc., the orientation of the cutting head could changewithout being actuated by the tractor operator. To prevent this aconventional friction brake is attached at the cutter head pivot pointin either embodiment illustrated. The brake illustrated in FIGS. 18-19shows the brake pads biased to the holding or braking position. Thefriction will be overcome by the hydraulic motor when a positive inputis directed by the operator; in the absence of operator input the cutterhead orientation should remain constant.

It will be apparent from the above that this invention provides a boomattachment which carries a suitable work unit at its outer end which canbe mounted at the rear end of a tractor by the usual three-point hitch.The work unit is angularly adjustable on the outer end of the boom. Theboom may be an articulated boom of two or more sections which are movedrelatively and relative to an upstanding support by cylinder and pistonunits which are supported at the side of the boom and support ratherthan in the angles therebetween which makes it possible to swing thework unit from one side of the tractor to the other withoutinterference. The boom may also be a single section with a mechanicaldrive to the work unit located so that it also will not interfere withits swinging movement on the tractor relative to its support making italso possible to move the work unit to one side or the other of thetractor.

Having thus described the invention in its preferred embodiment it willbe clear that modifications may be made to the apparatus withoutdeparting from the spirit of the invention. It is not intended that thewords and drawings used to describe the preferred embodiment be limitedon the invention. Rather it is intended that the invention be limitedonly by the scope of the appended claims.

Having thus described the invention what is claimed is:
 1. A boomattachment for supporting a work unit comprising a support, a boompivoted by a pivot at its inner end to said support for swingingmovement,a work unit supported on the outer end of said boom, and meansfor swinging said boom about said support pivot, said swinging meanscomprising a cylinder and piston unit connected at a laterally outwardlyextending pivot to said support and a laterally outwardly extendingpivot to said boom intermediate its inner and outer ends so it will bedisposed along the side cf the boom in a plane spaced from that of theboom and will not interfere with movement of the boom about its saidpivot to said support; said work unit being a mower comprising a supportpivoted to the boom, a plurality of vertical spindles carried by thesupport, a housing covering said spindles, cutters carried by thespindles in overlapping relationship to each other, and means fordriving said spindles, a forwardly facing slot in said housing, saidcutters being mounted in said housing to rotate with said spindles suchthat a part of each cutter projects forwardly through said slot duringsaid cutter rotation.
 2. An attachment according to claim 1 in which thepivots for said cylinder and piston unit are connected to the supportand boom for limited floating movement.
 3. An attachment according toclaim 1 in which the support is attached to a tractor by a transversebreakaway pivot which permits yielding in case the work unit strikes anobstruction.
 4. An attachment according to claim 1 in which the workunit is pivoted to the outer end of the boom, means for adjusting thework unit about the pivot.
 5. An attachment according to claim 4 inwhich the pivot for the work unit is transverse of the boom at its outerend so that said unit can swing from one side to the other of the boomat its outer end in order that the work unit can be adjusted past thecenter of the boom in either direction to exert a gravity force in thatdirection to aid in adjusting the boom about the support pivot.
 6. Anattachment according to claim 5 in which said adjusting means ishydraulically operated.
 7. An attachment according to claim 5 in whichsaid work unit comprises rotatable parts, a mechanical drive extendsalong the boom and is connected to drive said parts.
 8. An attachmentaccording to claim 5 in which the boom is composed of at least twoarticulated sections with the innermost section pivoted to said supportand the outermost section carrying said work unit, and means forcontrolling relative movement of the articulated sections, said meanscomprising a cylinder and piston unit connected to the respectivesections along the sides thereof so as not to interfere with relativemovement of the articulated sections.
 9. An attachment according toclaim 8 in which the cylinder and piston units are connected to therespective articulated sections intermediate their ends by pivots whichextend laterally outwardly from the sections.
 10. An attachmentaccording to claim 9 in which all of said parts are connected to theirrespective sections by floating supports for limited movement.
 11. Anattachment according to claim 9 in which the support is upstanding andis carried by a base which is attached to a tractor at its rear by ahitch and power takeoff, said boom being pivoted to said support formovement in a transverse plane, each of said cylinder and piston unitsbeing supported in a different transverse plane behind the transverseplane of said boom.
 12. An attachment according to claim 11 in which thebase is attached to the hitch of the tractor by breakaway joints whichpermit yielding of the base rearwardly when the work unit strikes anobstruction.
 13. An attachment according to claim 12 in which the baseis attached to said hitch at a transverse front rod about which it maypivot for forward and rearward swinging of the boom support, and acylinder and piston unit connected to said support and to said tractorfor controlling said swinging movement.
 14. An attachment according toclaim 13 in which the breakaway pivot is dispose at one end of saidpivot rod.
 15. An attachment according to claim 14 in which each jointcomprises a rocker arm pivoted to said base and to said hitch at saidpivot rod and means for biasing said arm forwardly by permittingrearward yielding if the work unit strikes an obstruction.
 16. Anattachment according to claim 4 in which said work unit is carried by apivot and support shaft mounted on the outer end of the boom.
 17. Anattachment according to claim 16 in which said means for adjusting thework unit comprises a rack and pinion carried by the boom for rotatingthe shaft.
 18. An attachment according to claim 16 in which a cylinderand piston unit is carried by the boom for actuation of the rack andpinion.
 19. An attachment according to claim 16 including a hydraulicmotor supported by the boom for rotating said shaft.
 20. An attachmentaccording to claim 19 in which the work unit has rotable parts, and amechanical drive extending along the boom to drive said parts.
 21. Anattachment according to claim 1 in which the cutters are in the form ofa plurality of radially extending horizontal flat blades mounted on ahub with adjacent hubs at different levels on the spindles so that theblades overlap.
 22. The attachment according to claim 1 wherein the boomis mounted on said support for swinging through a vertical arc of up toabout 210°.
 23. The attachment of claim 1 including a deflecting barextending downwardly from said housing toward said blades to cover partof said slot, said deflecting bar extending substantially the full widthof the mower and one end of said bar being curved toward the rear of themower,means for rotating said cutters to convey cut vegatation alongsaid deflecting bar to said curved end.
 24. The attachment of claim 23including a horizontal shield mounted on said housing and extendingabove and forward of said cutters.